1. Field of the Invention
This invention relates to a fuel control system for an engine, and more particularly to a fuel control system in which the amount of intake air during a transient state of operation of the engine can be detected more accurately
2. Description of the Prior Art
As disclosed, for instance, in Japanese Unexamined Patent Publication No. 58(1983)-25531, there has been known a fuel control system for an engine in which a basic fuel injection amount is calculated on the basis of the engine speed and the intake air amount, and the amount of fuel to be injected from a fuel injection valve is controlled according to the dulled value of the basic fuel injection amount during acceleration and deceleration, the dulled value being obtained by subjecting the basic fuel injection amount to a dulling process which comprises calculation of a weighted average.
That the dulled value of the basic fuel injection amount is used during a transient state of operation of the engine is because the amount of intake air as detected by an airflow meter is larger than the actual value during acceleration and is smaller than the actual value during deceleration (overshoot of the detected value) and if the detected value of the amount of intake air is used to calculate the basic fuel injection amount as it is detected, the air-fuel ratio can become overlean or overrich. Thus the dulling process is generally effected by such calculation of a weighted average that the preceding detected value is reflected in the present detected value by a predetermined proportion so that the detected value approximates the actual value.
However such a dulling process gives rise to a problem that, for example during acceleration, when the detected value of the amount of intake air (the output of the airflow meter) shown by the solid line in FIG. 6 converges after overshooting, the dulled value shown by the chained line in FIG. 6 can become larger than the detected value due to delay in change of the dulled value caused by influence of the preceding detected value and can deviate from the actual value more than the detected value as shown by the hatched portion in FIG. 6. This can be attended to by changing the dulling coefficient which governs the degree of reflection of the preceding detected value in the dulled value, but this approach results in only causing the detected value to slowly converge in a manner different from that of the actual value and is not practicable.